1. Field
This application relates generally to communications, and to techniques that enable multiple devices to access a wireless medium.
2. Background
In a wireless communication system multiple wireless devices may communicate with one another via signals having frequencies within a given radio frequency band. Here, provisions may be made to prevent transmissions from one device from interfering with transmissions from another device. For example, some systems employ media access control that allows only one device to use a given medium (e.g., a radio frequency band) at a time. One way of accomplishing this is to require that each device check the medium to determine whether another device is currently transmitting over the medium. If the medium is in use, the device will delay transmitting until a later time when the medium is not in use. Alternatively, some systems use a signaling technique such as spread spectrum that modifies transmitted signals to reduce the likelihood of transmissions from one device interfering with simultaneous transmissions of another device within the same frequency band.
Techniques such as these may be employed in a variety of wireless communication systems. An example of such a wireless communication system is an ultra-wide band system. In some implementations an ultra-wide band system may employ pulse signaling and bandwidths on the order of 500 MHz or more.
Various multiple access schemes have been proposed for use in ultra-wide band systems. One example is code division multiple access (“CDMA”) incorporating direct sequence, time hopping or an appropriate combination of these two schemes. Another example is frequency division multiple access (“FDMA”). Use of the ALOHA family of ad hoc multiple access techniques also have been proposed, for example, for intra-piconet conflict resolution. Chaos-based ultra-wide band systems have been proposed that use length division multiple access (“LDMA”) by varying the time duration of the ultra-wide band pulse.
In a typical application an ultra-wide band system is used for communication over relatively short distances. For example, ultra-wide band technology may be employed in a physical layer implementation for a body area network (“BAN”) or a personal area network (“PAN”). A wide variety of wireless devices having different power and data rate requirements may be deployed in such a BAN or a PAN. Consequently, various ultra-wide band receiver design approaches may be employed. For example, a receiver design may employ a coherent RAKE receiver design, a non-coherent energy detector design, or a transmitted reference design. Given the disparate requirements of applications such as these, a need exists for effective and adaptable multiple access techniques for wireless communications.